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X-HELO:	calimero.vinschen.de
Date:	Thu, 11 Aug 2016 16:13:05 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Cc:	Erik Bray <erik DOT m DOT bray AT gmail DOT com>
Subject:	Re: 2.5.1: kill(pid, sig) before waitpid() returns -1 for sig != 0
Message-ID:	<20160811141305.3em7tpcrxsushraa@calimero.vinschen.de>
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Mail-Followup-To:	cygwin AT cygwin DOT com, Erik Bray <erik DOT m DOT bray AT gmail DOT com>
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Hi Eric,

On Aug 11 11:51, Erik Bray wrote:
> [...]
> > Existing implementations vary on the result of a kill() with pid indica=
ting an inactive process (a
> > terminated process that has not been waited for by its parent). Some in=
dicate success on such a
> > call (subject to permission checking), while others give an error of [E=
SRCH]. Since the definition
> > of process lifetime in this volume of POSIX.1-2008 covers inactive proc=
esses, the [ESRCH] error
> > as described is inappropriate in this case. In particular, this means t=
hat an application cannot
> > have a parent process check for termination of a particular child with =
kill(). (Usually this is done
> > with the null signal; this can be done reliably with waitpid().)
>=20
> In response to the originally issue, this was fixed *specifically* for
> the case of kill(pid, 0).  But my reading of the above is that kill()
> should return 0 in this case regardless of the signal (modulo
> permissions, etc.).  On Linux, for example, when calling kill with pid
> of a zombie process the kernel will happily deliver the signal to the
> relevant task_struct; it will just never be acted on since the task
> will never run again.

I'm not sure why cgf only fixed that for sig 0 at the time, since, as
you noted, the text from POSIX-1.2008 does not state that this is
*restricted* to sig 0.

> The below (untested) patch demonstrates the change I'm suggesting,
> though I don't know what other code, if any, might be involved in
> this.

The original patch laid the groundwork by making sure that there are
two states, EXITED and REAPED.  Removing the explicit check for 0 is
the right thing to do, afaics, so I tested and applied your patch as is,
see=20
https://cygwin.com/git/?p=3Dnewlib-cygwin.git;a=3Dcommitdiff;h=3D86f79af827=
729f3968d8b3b8f860ac29d200da0d


Thanks,
Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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